Such kind of a conventional known cable extension unit can compensate attenuation of transmitted video signals by utilizing rectangular waves comprising horizontal and vertical synchronous signals corresponding to video signals as signals for compensation. Such cable extension unit can display good videos compensated on a video output machine which is arranged at a separate place with no complicated structure of the cable extension unit since it is not necessary to transmit signals for compensation separately from video signals, thereby actualizing effective presentation.
But, a rectangular wave the waveform of which is predetermined can not stably transmitted, and a video signal can not be correctly compensated since the rectangular wave comprising a horizontal or a vertical synchronous signal changes in its pulse width or a cycle, depending on resolution of an image or kinds of displays. In result, effective presentation may not be secured due to impossibility of stable compensation of video signals.
Since presentation can be made effective by outputting sounds, such as effective sounds and explanation of videos while displaying videos, the cable extension unit for outputting sounds to a video output machine as well as videos has been desired.
Then, the cable extension unit for stably compensating video signals by utilizing digital sound signals as signals for compensation, and for outputting good videos and sounds to a video output machine through which effective presentation can be actualized is desired to be developed.